A Magnetic Tactile Sensor Arrangement

The present invention relates to a magnetic tactile sensor arrangement. More particularly, the present invention relates to a magnetic tactile sensor arrangement suitable for use in a robotic end effector or similar.

In many fields, it is necessary to determine when contact has been made between objects, and relative motion of the objects in contact. For example, contact between a user's fingers and the surface of a touchpad/trackpad, contact between the hand of a user and a touch control panel or similar, etc.

In the field of robotics, when picking up or gripping objects with the end effector at the end of a robotic arm, it is important to know the location of the end effector relative to the object, and to be able to determine the point at which the end effector makes contact with the object. Similarly, it is also important to know the alignment of the end effector relative to the object when contact is made, and also the force exerted when a grip or similar is exerted. Such sensing is particularly important if the end effector and/or object to be grasped is/are relatively delicate.

Touchpads commonly work via capacitive sensing, where the change in capacitance is detected at the point where a finger contacts the pad. Capacitance sensing generally works very poorly with materials other than direct skin contact (for example stylus contact, or contact with a gloved finger).

Larger control surfaces or contact surfaces are becoming more common, for example in use on car dashboards or similar. In these applications, capacitive touch sensing may not be the most appropriate due to the larger surface area, the required robustness of the panel, and similar requirements.

A number of types of tactile sensor are already known in the field of robotics. For example, the “TacTip” sensor, developed at Bristol Robotics Laboratory, includes a flexible curved surface, on the inner (concave) surface of which are provided a number of pins (or papillae). A camera captures an image of the inner ends of the pins. When the surface is deformed by contact with an object, the inner ends of the pins move, and this movement can be seen by the camera. However, forming the curved surface with the pins is not straightforward; 3D printing is possible, but 3D printed materials are not particularly robust. Further, a considerable depth is needed to accommodate the pins, so the sensor has a minimum size, and may not be suitable for more delicate applications.

The “GelSight” sensor, developed at MIT's Computer Science and Artificial Intelligence Laboratory, uses a block of transparent rubber with a contact surface coated with a metallic paint. When the painted surface is pressed against an object, it conforms to the shape of the object. The side of the block opposite the contact surface is illuminated by three differently-coloured lights, and imaged by a camera. The camera captures images of the deformed surface in three different colours, and uses these to determine the shape of the object. Although this type of sensor gives a good image of the object, it does not provide a good representation of the tangential or normal forces involved in the contact, and does not allow small surface vibrations to be measured and localized. Further, since the metallic paint is exposed and contacted by the object, the sensor is vulnerable to wear. The sensor is also quite large, and again may not be suitable for more delicate applications.

1 2 FIGS.and 2 FIG. The use of magnetic sensor elements for tactile sensors is also known. Magnetic elements and a detector element or elements are embedded into a material layer, with the material in which the sensors are embedded being at least partly flexible and deformable. As the outer surface of the material makes contact with objects, it deforms, and the magnetic elements move relative to the detector element or elements. This relative movement of the magnetic elements and the detector allows changes in the magnetic field at the detector(s) to be measured, and used to calculate position and force. A typical arrangement for the material and the magnetic elements is shown in, with the sensor comprising magnetic elements sandwiched between an outer layer of flexible material, and an inner layer. The magnetic elements are held in place by gluing these to the inner surface of the outer layer with a suitable adhesive. However, as shown in, in an arrangement such as this, it can be difficult to retain the magnetic elements in the required position over extended periods of use, as these can become loosened and moved out of the required position due to shearing forces and other deformation forces exerted on the layers in use.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

It is an object of the present invention to provide a magnetic tactile sensor arrangement which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.

The term “comprising” as used in this specification and indicative independent claims means “consisting at least in part of”. When interpreting each statement in this specification and indicative independent claims that includes the term “comprising”, features other than that or those prefaced by the term may also be present. Related terms such as “comprise” and “comprises” are to be interpreted in the same manner.

As used herein the term “and/or” means “and” or “or”, or both.

As used herein “(s)” following a noun means the plural and/or singular forms of the noun.

Accordingly, in a first aspect the present invention may broadly be said to consist in a magnetic tactile sensor arrangement, comprising: a flexible inner layer and a flexible outer layer, the inner and outer layers sandwiched together adjacent to one another in use; at least one magnetic sensor element located substantially at or on the inner surface of the two layers, the magnetic sensor element comprising a magnetic sensor and sensor cup, the magnetic sensor locating into the cup in use, the sensor cup configured so that in use the majority of the magnetic sensor is enclosed within the sensor cup, the sensor cup formed from a ferrous material.

In an embodiment, the cup is arranged to face inwards.

In an embodiment, the sensor element is substantially flat, one side and the edge or edges of the sensor element substantially enclosed within the sensor cup.

In an embodiment, the sensor element comprises a coin-or disc-shaped magnetic element.

In an embodiment, the sensor element has a diameter of substantially 3 mm and a height/thickness of 0.5 mm.

In an embodiment, the magnetic sensor is formed from samarium cobalt.

In an embodiment, the sensor cup comprises a side wall and base, the sensor element and cup configured so that the side wall extends past the side wall/edge of the magnetic sensor.

In an embodiment, the thicknesses of the side wall and base are sufficient so that the cup material is not magnetically saturated by the magnetic sensor element.

In an embodiment, the wall has a thickness of substantially 0.45 mm, and the base of the cup has a thickness of substantially 0.4 mm.

In an embodiment, the base and outer edge of the wall are chamfered to a depth of substantially between 0.2 mm and 0.3 mm.

In an embodiment, the sensor element comprises a 3×0.5 mm samarium cobalt magnet.

In an embodiment, one or both of the inner and/or outer layer are formed from a flexible elastomer material.

In an embodiment, one or both of the inner and/or outer layer are formed from silicone.

In an embodiment, at least one sensor holder is integrally formed with one of the layers and located between the layers, the sensor holder configured to receive the magnetic sensor element so that in use the magnetic sensor element remains in position within the holder and move with the holder.

In an embodiment, the at least one sensor holder comprises a cavity formed in the layer.

In an embodiment, the cavity has a depth of substantially 1 mm.

In an embodiment, the at least one sensor holder comprises a protrusion extending from and forming part of the inner surface of a layer, the cavity formed within the protrusion.

In an embodiment, the protrusion is substantially twice the height of the depth of the cavity.

In an embodiment, the protrusion has the general form of a cut-off or truncated cone.

In an embodiment, the cut plane of the cone is substantially parallel to the main body of the layer.

In an embodiment, the outer wall or slope of the cone is angled at between 45 and 60 degrees to the cut plane.

In an embodiment, the protrusion is substantially circular in plan view, the cavity substantially central within the protrusion in plan view.

In an embodiment, the overall height of the cut cone is substantially 2 mm.

In an embodiment, the protrusion is formed on the inner surface of the outer layer.

In an embodiment, the at least one sensor holder comprises a plurality of sensor holders.

In an embodiment, the sensor holders are arranged in at least one substantially straight line.

In an embodiment, the sensor holders are arranged in parallel lines.

In an embodiment, the magnetic tactile sensor arrangement further comprises at least one Hall effect sensor located in or on the inner layer.

In an embodiment, the at least one Hall effect sensor comprises a Hall effect sensor or sensors, each of the Hall effect sensor or sensors associated with a magnetic sensor element.

In an embodiment, the magnetic tactile sensor arrangement is configured so that the Hall effect sensor or sensors are located substantially between 1 mm-2 mm from the inner surface of an associated magnetic sensor element.

In a second aspect, the invention may broadly be said to consist in a magnetic tactile sensor arrangement, comprising: a flexible inner layer and a flexible outer layer, the inner and outer layers sandwiched together adjacent to one another in use; at least one sensor holder integrally formed with one of the layers and located between the layers, the sensor holder configured so that a sensor located in the holder will, in use, remain in position within the holder and move with the holder.

In an embodiment, one or both of the inner and/or outer layer are formed from a flexible elastomer material.

In an embodiment, one or both of the inner and/or outer layer are formed from silicone.

In an embodiment, the at least one sensor holder comprises a cavity formed in the layer.

In an embodiment, the cavity has a depth of substantially 1 mm.

In an embodiment, the at least one sensor holder comprises a protrusion extending from and forming part of the inner surface of a layer, the cavity formed within the protrusion.

In an embodiment, the protrusion is substantially twice the height of the depth of the cavity.

In an embodiment, the protrusion has the general form of a cut-off or truncated cone.

In an embodiment, the cut plane of the cone is substantially parallel to the main body of the layer.

In an embodiment, the outer wall or slope of the cone is angled at between 45 and 60 degrees to the cut plane.

In an embodiment, the protrusion is substantially circular in plan view, the cavity substantially central within the protrusion in plan view.

In an embodiment, the overall height of the cut cone is substantially 2 mm.

In an embodiment, the protrusion is formed on the inner surface of the outer layer.

In an embodiment, the at least one sensor holder comprises a plurality of sensor holders.

In an embodiment, the sensor holders are arranged in at least one substantially straight line.

In an embodiment, the sensor holders are arranged in parallel lines.

In an embodiment, the magnetic tactile sensor arrangement further comprises a magnetic sensor element configured to locate into the sensor holder, the magnetic sensor element comprising a magnetic sensor and sensor cup, the sensor locating into the cup in use, the sensor cup configured so that in use the majority of the sensor element is enclosed within the sensor cup, the sensor cup formed from a ferrous material.

In an embodiment, the sensor element is substantially flat, one side and the edge or edges of the sensor element substantially enclosed within the sensor cup.

In an embodiment, the sensor element comprises a coin-or disc-shaped magnetic element.

In an embodiment, the sensor element has a diameter of substantially 3 mm and a height/thickness of 0.5 mm.

In an embodiment, the magnetic sensor is formed from samarium cobalt.

In an embodiment, the sensor cup comprises a side wall and base, the sensor element and cup configured so that the side wall extends past the side wall/edge of the magnetic sensor.

In an embodiment, the thickness of the wall and base is sufficient so that the cup material is not magnetically saturated by the magnetic sensor element.

In an embodiment, the wall has a thickness of substantially 0.45 mm, and the base of the cup has a thickness of substantially 0.4 mm.

In an embodiment, the base and outer edge of the wall are chamfered to a depth of substantially between 0.2 mm and 0.3 mm.

In an embodiment, the cup is arranged within the sensor holder so that most or all of those parts of the sensor element not enclosed within the sensor cup face inwards. In an embodiment, the sensor element comprises a 3×0.5 mm samarium cobalt magnet.

In an embodiment, the magnetic tactile sensor arrangement further comprises at least one Hall effect sensor located in or on the inner layer.

In an embodiment, the at least one Hall effect sensor comprises a Hall effect sensor or sensors, each of the Hall effect sensor or sensors associated with a magnetic sensor element.

In an embodiment, the magnetic tactile sensor arrangement is configured so that the Hall effect sensor or sensors are located substantially between 1 mm-2 mm from the inner surface of an associated magnetic sensor element.

In a third aspect the invention may broadly be said to consist in a robotic end effector comprising a magnetic tactile sensor arrangement as outlined in any one of the second aspect statements above.

In a fourth aspect, the invention may broadly be said to consist in a robotic arm comprising an end effector as outlined in the third aspect statement above.

In a fifth aspect, the invention may broadly be said to consist in a sensor cup for use with a magnetic tactile sensor assembly, comprising: a cup body configured to receive a magnetic sensor, the cup body configured so that in use the majority of the magnetic sensor is enclosed within the sensor cup, the sensor cup formed from a ferrous material.

In an embodiment, the cup body comprises a side wall and base, the thickness of the wall and base sufficient so that the cup material is not magnetically saturated by a magnetic sensor located in the cup body.

In an embodiment, the side wall is configured so that in use with a magnetic sensor located in the cup body, the side wall extends past the side wall/edge of the magnetic sensor.

In an embodiment, the cup body is substantially cylindrical.

In an embodiment, the wall has a thickness of substantially 0.45 mm, and the base of the cup has a thickness of substantially 0.4 mm.

In an embodiment, the base and outer edge of the wall are chamfered to a depth of substantially between 0.2 mm and 0.3 mm.

In a sixth aspect, the invention may broadly be said to consist in a robotic end effector comprising at least one sensor cup as outlined in any one of the fifth aspect statements above.

In a seventh aspect, the invention may broadly be said to consist in a robotic arm comprising an end effector as outlined in the sixth aspect statement above.

With respect to the above description then, it is to be realised that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Embodiments of the invention, and variations thereof, will now be described in detail with reference to the figures.

4 One preferred embodiment of the present invention uses magnetic sensor assembliesthat in this embodiment are embedded into an end effector or similar that forms part of a robotic hand. This will be described in detail below.

The invention is also suitable for use in a number of other applications, which are detailed at the end of the description.

3 FIG. 1 2 3 4 As shown in, the magnetic tactile sensor arrangement used with the tactile sensor in an end effectorcomprises three main elements: an inner layer; an outer layer, and; magnetic sensor assemblies.

2 3 2 3 The inner and outer layersandare formed of a flexible elastomer material, such as for example silicone. The inner and outer layers,are sandwiched together in use. In this embodiment, the two layers are directly adjacent to one another. However, in other embodiments, the two layers could be separate by one or more ‘filling’ layers, or central layers. ‘Sandwiched’ as used in this specification should be taken to mean that the inner and outer layers are either directly adjacent to one another, or separated by one or more layers.

3 5 3 3 3 FIG. This embodiment of outer layercomprises a number of sensor holdersthat are integrally formed as part of the outer layer, on the inner surface of the outer layer, as shown in.

As noted, there is an inner layer and an outer layer. Where ‘inner surface’ or similar is used in this specification, this should be taken to mean on the inside of, or between, the two sandwiched layers, e.g. that side of the outer layer that faces towards the inner layer.

In alternative forms, the sensor holders could be formed on the inner surface of the inner layer (that side of the inner layer that faces towards the outer layer), or holders could be formed on both the inner sides of both of the inner and outer layer.

7 FIG. 5 3 5 As shown in, in an embodiment the holderscan be arranged in substantially parallel lines along the inner surface of the outer layer. However, the sensor holderscan be positioned relative to one another as required, in numbers as required, and in a pattern as required, for any particular use. A single holder could also be used, if a single sensor only is required in a particular embodiment.

5 FIG. 5 FIG. 5 5 3 6 10 5 6 shows a cross-section view of a holder. In the preferred form, each of the sensor holderscomprises a bulge or protrusion on the inner surface of the outer layerthat has the general form of a cut-off or truncated cone, with a central cavity. In the preferred embodiment the ‘cut’ plane of the cone (shown by the dotted line on) is substantially parallel to the outer surface of the outer layer. The outer wall or slopeof the holderis at an angle to the ‘cut’ plane, and for variations this angle can be between 45 and 60 degrees. The central cavityis circular in plan view, and has a depth of substantially 1.0 mm, which is approximately half of the overall height of the cut cone.

4 FIG. 5 4 6 4 3 In use, as shown in, the holderacts to retain a magnetic sensor assemblyembedded/located in the central cavity, so that the magnetic sensor assemblyis in use located in the required position on the inner surface of the outer layer, and is held in position during repeated use without becoming loose and out of position.

The sensor holders for the preferred embodiment as described above are bulges or protrusions that extend from the surface of the layer. In alternative forms, these could be formed as cavities within the layer itself—that is, the layer would not require bulges or protrusions in order for the sensor holders to be formed directly into the layer. ‘Between’ as used in this specification should be taken to mean substantially directly at the contact surface between the inner and outer layers, or slightly to one side of/adjacent to this.

4 7 8 Each of the magnetic sensor elementscomprises a magnetic sensorand sensor cup.

7 9 FIG. The magnetic sensorcomprises a coin-or disc-shaped magnetic element, having a diameter in the preferred embodiment of 3 mm and a height/thickness of 0.5 mm. As shown in, the magnetic field lines for the unrestrained sensor extend over and around the magnet, with the poles of the magnet located on each of the opposed faces of the disc. In the preferred embodiment, the magnetic sensor is formed from samarium cobalt.

7 8 7 8 8 7 8 7 7 8 8 8 7 13 11 FIG. The magnetic sensorand sensor cupare formed so that the magnetic sensorlocates snugly into the sensor cup. The sensor cupis configured so that with the magnetic sensorsnugly located in the sensor cup, the sensoris fully surrounded/enclosed at it's edge and on that flat side facing towards the ‘inside’ of the cup (that side towards the outer side of the outer layer in use). The opposed flat side of the sensoris fully free (that side which in use faces inwards, ‘out’ of the cup). The sensor cupis sized so that the side wall of the cupextends slightly past the side wall/edge of the magnetic sensor, and has an overall height of substantially 1 mm, as shown by dimension ‘’ on.

8 8 11 12 11 FIG. Detail of the sensor cupis shown in. In the preferred embodiment the cuphas a wall thickness of 0.45 mm (shown by dimension ‘’), and a base thickness of 0.4 mm (shown by dimension ‘’). The base and outer edge of the wall are chamfered to a depth of substantially between 0.2 mm and 0.3 mm. The wall/base thickness is intended to be sufficient so that the cup material is not magnetically saturated. So, for example in the preferred embodiment, the wall thickness is at least 0.4 mm for a 3×0.5 mm samarium cobalt magnet. The wall/base thickness can be varied for variations of the sensor, depending on the strength of the magnet used in a particular variation/embodiment.

8 7 8 10 FIG. The sensor cupis formed of a ferrous material, which constrains the magnetic field from the magnetic element. In use, with the magnetic sensorlocated into the sensor cup, the magnetic field is constrained on the cup side/enclosed side as shown in, with the field lines more concentrated on the constrained side than they are on the free or open side.

The magnetic field lines are significantly less concentrated on the opposite side (the side that faces the external surface of the tactile sensor). This helps to reduce any magnetic fields which would travel through ferrous materials in the vicinity of the tactile sensor, affecting the magnetic field on the reverse side (towards the Hall sensor). This helps to reduce any offsets on the tactile sensor caused by nearby ferrous objects. This also assists with reducing the magnetic field on the outwards-facing surface, which could for example lead to undesirable results such as the unwanted collection of loose metallic objects such as metal swarf/filings on the outer surface.

8 7 7 8 The sensor cupas described above is sized so as to be suitable for constraining a particular size of magnetic sensor. The sizes of both the magnetic sensorand cupcan be changed as required, so that the magnetic field is suitable for a particular purpose, and is suitably constrained for that particular use. Different types and shapes of magnet can also be used, with the shape and size of the cup adjusted accordingly.

8 6 8 In use, the cupis glued into the cavity. The shape of the interior of the cavity is configured to allow the adhesive to bond around the steel of the external surfaces of the cup.

2 3 4 FIG. In use, as the tactile sensor contacts items, the inner and outer layersandwill deform in a similar manner to that shown in.

4 8 FIGS.and 4 FIG. 9 2 7 7 9 7 9 7 9 As shown in, a Hall effect sensoris embedded in the inner elastomer layerin a position relative to the magnetic element of the magnetic sensorthat is substantially in line with the central axis of the circular coin of the magnetic sensor. The Hall effect sensoris in a preferred variation located a distance of substantially 1 mm-2 mm from the inner surface of the magnetic sensor. The Hall effect sensoris used to measure changes in the magnetic field from the magnetic sensoras this moves relative to the Hall effect sensor, as the elastomer layers are deformed as for example shown in.

8 9 10 FIG. The ‘open or unconstrained side of the cupfaces the Hall effect sensor. The constraining effect of the cup has the effect of producing a more powerful magnetic field for the Hall effect sensor to measure, resulting in a higher sensitivity (see for example).

9 The Hall effect sensoris connected to a controller or similar (not shown) which receives the readings from the Hall effect sensor and uses these to help assess position and grip of the end effector.

104 102 103 104 5 7 3 1 2 FIGS.and 2 FIG. 4 FIG. In the prior art arrangement (magnetic elementsand inner and outer layers,as shown in) and as outlined above, the magnetic elementscan come unstuck and out of position during use. In the embodiment of the present invention, the sensor holdersact to keep the magnetic sensorsin the required location on the inner surface of the outer layerduring use, and increase the ability of the sensor to endure heavy impacts and forces. The ‘peeling’ force shown inis diverted to a sheering force (as shown in) which is more easily resisted.

In the description above, the invention is particularly described in relation to an end effector for a robotic arm. However, the invention should not be taken as being limited to this particular use. It should be noted that the invention is suitable for use in many other applications where a touch sensitive system is required. For example, the system could be used to form a, or part of, a touchpad, a keyboard (either for typing, drafting, or a musical instrument), a control panel (such as those in automobiles or similar) and many other similar uses.

To achieve this, the layers of material that contain the magnetic sensor arrangement can be arranged in a flat sheet, or as a sheet shaped for the particular purpose required (e.g. over a curved surface, or wrapped around a cylinder or sphere, or similar). The arrangement could also be used for individual buttons or similar (although it will be appreciated that the invention is also suited to sliding contact or moving contact over a surface, or similar). When a user is in contact with the surface, this will cause movement of the magnetic element or elements away from their neutral positions, and relative to the Hall sensor or sensors. This detected output, when received at a central controller or similar, can be used to assess user input, and therefore required output from the controller.